Workers exposed to asbestos have an increased incidence of bowel cancer as well as an increased incidence of lung cancer and mesothelioma. A pathologic study of a sample of asbestos-related bowel cancers revealed a very unusual type of chronic colitis underlying and apparently preceding the cancer. The proposal is to study asbestos cancers and precursor lesions in detail. Human material will be reviewed. In addition, the intestines of rats fed asbestos will be studied in detail to determine the full range and time sequence of asbestos-related pathology. Following this, the asbestos lesions will be studied as possible preferential sites for induction by known bowel carcinogens.